GH-43573: [C++] Copy bitmap when casting from string-view to offset string and binary types by crystalxyz · Pull Request #44822 · apache/arrow

crystalxyz · 2024-11-24T03:10:55Z

Rationale for this change

Use CopyBitmap to optimize performance in string casting from string-view to offset string.

What changes are included in this PR?

Originally, the way we create the bitmap is by appending one bit at a time, which is slow. Since casting should not change the values in bitmap, this feature takes advantage of CopyBitmap to create the entire bitmap at once.

Then, to create offsets and buffer array, I use TypedBufferBuilder as suggested in the original comment #43302 (comment).

Are these changes tested?

The original unit tests have passed.

Are there any user-facing changes?

No, the casting behavior should remain unchanged.

closes #43573

GitHub Issue: [C++] Copy bitmap all at once when casting from string-view to offset string and binary types #43573

github-actions · 2024-11-24T03:11:20Z

⚠️ GitHub issue #43573has been automatically assigned in GitHub to PR creator.

mapleFU · 2024-11-24T05:40:37Z

+ if (input.offset == output->offset) {
+ output->buffers[0] = input.GetBuffer(0);
+ } else {
+ if (input.buffers[0].data != NULLPTR) {


// When the offsets are different (e.g., due to slice operation), we need to check if // the null bitmap buffer is not null before copying it. The null bitmap buffer can be // null if the input array value does not contain any null value.
Do we also need a comment here?

Can you copy and paste this utility function [1] to this compilation unit and call it from here instead?
[1] https://github.com/apache/arrow/blob/main/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc#L42
(Later the utility could be moved to a .h so it's callable from anywhere and inlinable. But I'm suggesting a copy because it's tricky to name this function in an informative and non-error-prone way.)

Co-authored-by: mwish <maplewish117@gmail.com>

felipecrv

This looks great. Asking for some tweaks.

felipecrv · 2024-12-10T13:29:13Z

+ if (input.offset == output->offset) {
+ output->buffers[0] = input.GetBuffer(0);
+ } else {
+ if (input.buffers[0].data != NULLPTR) {


Can you copy and paste this utility function [1] to this compilation unit and call it from here instead?
[1] https://github.com/apache/arrow/blob/main/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc#L42
(Later the utility could be moved to a .h so it's callable from anywhere and inlinable. But I'm suggesting a copy because it's tricky to name this function in an informative and non-error-prone way.)

mapleFU

General LGTM, thanks!

felipecrv · 2025-01-29T17:15:05Z

@mapleFU don't you want take this to the finish line? Unless @CrystalZhou0529 is available to implement the final changes.

crystalxyz · 2025-02-07T19:14:00Z

Thanks for reviewing it! Sorry for falling behind on this PR. I will implement the final changes now.

Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

crystalxyz · 2025-02-07T19:58:04Z

Hi @felipecrv @mapleFU, I have just committed the requested changes. Please take another look and let me know if it looks reasonable!

mapleFU

General LGTM!

mapleFU · 2025-02-14T17:22:32Z

@felipecrv Would you mind take a look? Or I just move forward?

mapleFU · 2025-02-20T14:30:51Z

@pitrou @zanmato1984 would you mind take a look? This optimization is not complex

pitrou · 2025-02-20T14:34:12Z

Are the CI failures related?

mapleFU · 2025-02-20T14:47:46Z

Let me rerun to see it

pitrou · 2025-02-20T15:16:56Z

Yeah, GetNullBitmapBuffer is getting defined twice in unity builds, it seems.

pitrou · 2025-02-20T15:37:47Z

The CI failures need fixing but, other than that, this PR is looking very good. I get a 2x improvement on some Python micro-benchmarks:

before:

>>>a=pa.array(([b'foobar']*100+[None])*100, type=pa.binary_view())
>>>b=a.cast(pa.binary())
>>>%timeita.cast(pa.binary())
136μs ± 461nsperloop (mean ± std. dev. of7runs, 10,000loopseach)
>>>%timeitb.cast(pa.binary_view())
18.4μs ± 21nsperloop (mean ± std. dev. of7runs, 100,000loopseach)

after:

>>>a=pa.array(([b'foobar']*100+[None])*100, type=pa.binary_view())
>>>b=a.cast(pa.binary())
>>>%timeita.cast(pa.binary())
51.6μs ± 256nsperloop (mean ± std. dev. of7runs, 10,000loopseach)
>>>%timeitb.cast(pa.binary_view())
19.5μs ± 458nsperloop (mean ± std. dev. of7runs, 100,000loopseach)

(also showing the binary -> binary_view conversion for comparison)

mapleFU · 2025-02-20T15:53:47Z

Yeah, GetNullBitmapBuffer is getting defined twice in unity builds, it seems.

Aha scalar_cast_nested.cc also defined a part of this

mapleFU · 2025-02-20T16:03:59Z

+ return in_array.GetBuffer(0);
+ }
+
+ if (in_array.offset % 8 == 0) {


Add a SliceBuffer

mapleFU · 2025-03-26T09:47:14Z

@pitrou I've move helper fn to a common place, would you mind take a look?

pitrou

This mostly looks good to me, I posted a small suggestion for improvement.

pitrou

Thanks for the update! Feel free to merge if CI is green @mapleFU

conbench-apache-arrow · 2025-03-27T21:25:33Z

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit a42edc0.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 23 possible false positives for unstable benchmarks that are known to sometimes produce them.

…fset string and binary types (apache#44822) ### Rationale for this change Use `CopyBitmap` to optimize performance in string casting from string-view to offset string. ### What changes are included in this PR? Originally, the way we create the bitmap is by appending one bit at a time, which is slow. Since casting should not change the values in bitmap, this feature takes advantage of `CopyBitmap` to create the entire bitmap at once. Then, to create offsets and buffer array, I use `TypedBufferBuilder` as suggested in the original comment apache#43302 (comment). ### Are these changes tested? The original unit tests have passed. ### Are there any user-facing changes? No, the casting behavior should remain unchanged. closes [ apache#43573 ](apache#43573) * GitHub Issue: apache#43573 Lead-authored-by: Crystal Zhou <crystal.zhouxiaoyue@hotmail.com> Co-authored-by: mwish <maplewish117@gmail.com> Co-authored-by: Crystal Zhou <45134936+CrystalZhou0529@users.noreply.github.com> Co-authored-by: Crystal <45134936+CrystalZhou0529@users.noreply.github.com> Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com> Signed-off-by: mwish <maplewish117@gmail.com>

Optimize string view to offset string cast
14d7d5c

github-actionsBot added the Component: C++ label Nov 24, 2024

crystalxyz marked this pull request as draft November 24, 2024 03:11

github-actionsBot added the awaiting review Awaiting review label Nov 24, 2024

crystalxyz marked this pull request as ready for review November 24, 2024 03:12

mapleFU reviewed Nov 24, 2024
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github-actionsBot added awaiting committer review Awaiting committer review and removed awaiting review Awaiting review labels Nov 24, 2024

pitrou requested a review from felipecrv November 27, 2024 13:29

crystalxyzand others added 3 commits November 30, 2024 17:41

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc
3d6b715
Co-authored-by: mwish <maplewish117@gmail.com>

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc
5c4a5d1
Co-authored-by: mwish <maplewish117@gmail.com>

Fix allocation of data buffer size
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felipecrv requested changes Dec 10, 2024
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Comment threadcpp/src/arrow/compute/kernels/scalar_cast_string.cc

crystalxyzand others added 2 commits February 7, 2025 14:18

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc
6341169
Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

Update cpp/src/arrow/compute/kernels/scalar_cast_string.cc
4312be2
Co-authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>

github-actionsBot added awaiting change review Awaiting change review and removed awaiting changes Awaiting changes labels Feb 7, 2025

Copy GetNullBitmapBuffer to own file and call it
5c262a9

mapleFU approved these changes Feb 8, 2025
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Comment threadcpp/src/arrow/compute/kernels/scalar_cast_string.cc Outdated

mapleFU requested a review from felipecrv February 14, 2025 17:20

Merge branch 'main' into pr-44822
77c3d37

Trying to fix ci
68fab84

mapleFU reviewed Feb 20, 2025
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mapleFU requested a review from pitrou February 25, 2025 13:27

mapleFU added 2 commits March 26, 2025 17:40

Merge branch 'main' into 43573-copy-bitmap-when-cast-string
b7386b5

move GetOrCopyNullBitmapBuffer to util_internal.h
9827e3e

pitrou reviewed Mar 26, 2025
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Comment threadcpp/src/arrow/compute/kernels/scalar_cast_string.cc Outdated

pitrou reviewed Mar 26, 2025
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using VisitVoid instead of VisitStatus
36c6001

mapleFU force-pushed the 43573-copy-bitmap-when-cast-string branch from 88c039d to 36c6001Compare March 27, 2025 03:05

mapleFU requested a review from pitrou March 27, 2025 09:31

pitrou approved these changes Mar 27, 2025
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mapleFU merged commit a42edc0 into apache:mainMar 27, 2025

mapleFU removed the awaiting change review Awaiting change review label Mar 27, 2025

mapleFU mentioned this pull request Mar 27, 2025
[C++] Copy bitmap all at once when casting from string-view to offset string and binary types #43573
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